Begin by exploring triangles and quadrilaterals.
As you drag the vertices to reshape these polygons, occasionally play the
animated clip in the lower right corner.

- Is there a different result for different shapes?
- Test your conjecture by creating a square, rhombus, parallelogram, and other
quadrilaterals. For each type of shape, play the movie. How does the result
change?

Use the applet to examine pentagons, hexagons, heptagons and
octagons, too. Do you notice a pattern? How does the sum of the angles change as
the number of sides changes?

- What happens to the angle sum as you reshape the polygon by moving the
original vertices?
- Find a formula that relates the number of sides (
*n*) to the sum of the
interior angle measures?